I. Field of the Invention
This invention relates generally to an implantable, programmable, cardiac stimulating apparatus and method that non-intrusively determines the pulse pressure of a patient""s heart. The determined pulse pressure may be utilized, for example, to enhance cardiac performance. The cardiac performance may be enhanced by first manipulating the pacing rate and pacer timing intervals between intrinsic or paced stimulations of pre-selected chambers of the patient""s heart over a plurality of periods, then determining the pulse pressure during each period, identifying the pacer timing interval and/or pacing rate that results in the greatest pulse pressure, and finally setting the cardiac stimulator to the timing interval associated with the greatest pulse pressure to thereby increase cardiac performance.
II. Discussion of the Related Art
The cardiac output of a patient""s heart may be reduced as a result of defects, failure, disease, ageing, or other cardiac disorders or anomalies. Reduced cardiac output can lead to shortness of breath, restricted movement, and even death. Over the years various devices including pacers and defibrillators have been used to assist and/or alter the intrinsic contractions and pacing of the heart in order to increase the cardiac output of the heart. The pacer, for example, typically includes a pulse generator, power supply, microprocessor based controller, and an electrical lead of suitable construction coupled to the pulse generator for unipolar or bipolar pacing.
Various methods have been devised to maximize cardiac output, wherein the maximum cardiac output is correlated with a measured pulse pressure. Typically, the pulse pressure is measured via cardiac catheterization or through a pressure sensor positioned on a lead. A pacer of suitable construction is required in order to receive a signal from the pressure sensor and correlate the received signal with cardiac output. At times it may become necessary to replace an already implanted pacemaker with a pacer capable of correlating the maximum cardiac output with the measured pulse pressure. Ideally, replacement of the pacer would not require placement of additional leads or lead ablation and replacement.
In U.S. Pat. 4,566,456 issued to Koning et al., a device is described that adjusts a pacer rate relative to right ventricular systolic pressure. The right ventricular systolic pressure is measured by a piezoelectric pressure sensor mounted on a lead. Koning et al. does not provide for a device or method that non-intrusively determines the pulse pressure of a patient""s heart. The Koning et al. device requires a lead having a pressure sensor coupled thereto, and thus requires replacement or use of the specialized lead in conjunction with the disclosed pacer.
In U.S. Pat. 5,549,650 issued to Bornzin et al., a device is described for providing hemodynamically optimal pacing therapy. The device apparently includes a cardiac wall motion sensor which must be incorporated into an implantable lead. The rate of pacing therapy is controlled by the Bornzin et al. device as a function of the cardiac wall velocity signals and cardiac wall displacement signals (mechanical activities of the heart generally) transmitted by the cardiac wall motion sensor. The Bornzin et al. device does not provide hemodynamically optimal pacing therapy by non-invasively measuring the hemodynamic pulse pressure of the heart. The Bornzin et al. device requires replacement or use of a specialized lead in conjunction with its pacing device. Hence, there is a need for a pacemaker that non-intrusively determines the pulse pressure of a patient""s heart. The present invention addresses these and other needs.
In accordance with the present invention, a cardiac stimulation device is provided which is capable of non-intrusively determining a hemodynamic pulse pressure of the patient""s heart. The cardiac stimulating device may be programmed to function in a preset pacing mode having a preset pacing rate and timing interval to optimize cardiac performance of a patient""s heart. The cardiac stimulation device is capable of operating in any of a plurality of pacing modes, including A-V pacing, V-V pacing and A-A pacing, wherein the A-V pacing mode may include AR-VR pacing, AR-VL pacing, AL-VR pacing, AR-VRL pacing, AL-VRL pacing, and AL-VL pacing.
The cardiac stimulation device includes a pulse generator for stimulating a patient""s heart in a preselected pacing mode, a power supply, a microprocessor-based controller, and an accelerometer sensor, all of which are enclosed in an implantable casing. An internal or external cardiac electrogram or other conventional device for identifying cardiac cycles of a patient""s heart is coupled to the microprocessor based controller. The microprocessor-based controller is coupled to both the accelerometer and the pulse generator for receiving an input from the former and providing control signals to the latter.
The accelerometer sensor is electrically coupled to the microprocessor based controller and the accelerometer transmits a signal to the controller associated with fluid and myocardial accelerations of the patient""s heart. A filtering means is coupled to the accelerometer for filtering and conditioning the signal transmitted by the accelerometer to produce a waveform related to a pulse pressure within the patient""s heart.
The microprocessor based controller includes a linear prediction means (utilizing Levinson""s Algorithm well known to those skilled in the art) which predicts values associated with the waveform, wherein the linear prediction means includes a means for auto-regressive analysis of the preconditioned accelerometer energy signal using an algorithm which is described below in greater detail. The microprocessor based controller also includes: a bandwidth determining means for determining a bandwidth from predicted values of the waveform, center frequency determining means for determining a center frequency from predicted values of the waveform, means for calculating an amount indicative of pulse pressure from the determined bandwidth and center frequency, and analyzing means for analyzing the amounts indicative of pulse pressure over corresponding cardiac cycles.
The calculated value associated with pulse pressure may be analyzed by the microprocessor over a preselected number of cardiac cycles and for a plurality of preselected timing intervals, wherein the timing interval is a measured time between at least one of intrinsic and paced stimulations of pre-selected chambers of the heart. The value associated with pulse pressure corresponding with each timing interval is then compared to determine which timing interval results in the greatest pulse pressure. The pacer may then automatically reset the timing interval to this xe2x80x9cmaximumxe2x80x9d timing interval.
The analysis and comparison of the accelerometer signal preferably occurs when the patient is at rest, the quiescent period. The accelerometer signal may also be used to determine the period of quiescent activity. Analyzing the accelerometer signal during the period of quiescent activity minimizes motion artifact in the accelerometer signal. Further, analyzing the signal during the period of quiescent activity allows the measurements to be taken during relative steady state hemodynamic conditions.
Those skilled in the art will recognize that the accelerometer and other components may be mounted externally, linking these components with the microprocessor by telemetry. However, without limitation, a single self-contained implantable cardiac stimulating device including all of these components is preferred.
It is accordingly a principal object of the present invention to provide a cardiac stimulation device capable of dual chamber pacing which non-intrusively determines a value indicative of the pulse pressure for a selected cardiac cycle.
Another object of the present invention is to provide a cardiac stimulator which maximizes cardiac performance through non-invasive means by determining a value indicative of the cardiac pulse pressure from a signal of an accelerometer.
A further object of the present invention is to optimize cardiac performance based on an analysis and comparison of non-intrusively measured values indicative of pulse pressure over a plurality of preselected timing intervals, to thereby determine the optimum timing interval of the cardiac stimulator.
Still another object of the present invention is to provide a method for optimizing cardiac performance by non-intrusively determining the optimal timing interval based on the mechanical performance of the patient""s heart.
These and other objects as well as these and other features and advantages of the present invention will become readily apparent to those skilled in the art from a review of the following detailed description of the preferred embodiment especially when considered in conjunction with the claims and accompanying drawings in which like numerals in the several views refer to corresponding parts.